The reason why people are seeing Health stacking as so important, is because, of yes. World of Warcraft, where health stacking is the be all and end all of pvp.(along with resilience etc)
But, as people have stated, Health stacking is map, dg, and build dependant, for instance, health stacking on a rook combat build, is a little bit pointless, it may be good early game, but late game, you're just going to be a punching bag.
Same as health stacking on a QoT is absolutely pointless in most situations.
Same with TB, as late game, when you're sat there with 13k health and 3 damage abilities, someone with more constant damage will rip you apart, or someone with interupts will fuck you up, no matter how much health you have.
Its a personal choice on health stacking, but sometimes, carrying speed, and offensive abilities is worth the trade off. Especially with some DG's late game.